1. Field of the Invention:
The present invention relates to a foamed abrasive element and to a method of producing the same.
2. Description of the prior arts:
Abrasive wheels which have been conventionally known include vitrified abrasive wheels, bakelite ones (resinoid ones), rubber ones, oxychloride ones, and synthetic resin ones containing unsaturated polyester resins. These abrasive wheels have a high compressive modulus and are rigid. Therefore they fully exhibit their performance in precision processing and heavy duty abrading but cannot provide ability close to that in abrading with endless belts typifying abrasive papers and cloths which are main products in abrasive processing. This is because the conventional abrasive wheels have high compressive modulus as given below and highly rigid and hence they are poor in following-up fitness to workpieces.
______________________________________ Kind of abrasive Compressive modulus wheel Type No. (kg/cm.sup.2) ______________________________________ Vitrified WA120L 7 .times. 10.sup.5 Abrasive Wheel WA800K 4 .times. 10.sup.4 Resinoid WA120L 3 .times. 10.sup.5 Abrasive wheel C100H 1.2 .times. 10.sup.4 ______________________________________
On the other hand, the compressive modulus of rigid rubber rollers of contact wheels for abrasive belts can have a wide range of 10.sup.2 to 10.sup.5 kg/cm.sup.2 by varying the properties of the rigid rubbers. In general, although depending on materials and shapes of workpieces, the compressive modulus of the contact wheels for abrasive belts is about 10.sup.3 kg/cm.sup.2 and can exhibit an excellent abrasive performance with following-up fittness. However, the abrasive papers and cloths (abrasive belts) cannot have the concentration of abrasive grains and the thickness of layer of abrasive grains as high as those of the abrasive wheels. Therefore they have a short useful life and must be exchanged frequently, which is not economical and leads to a long loss time. These defects are serious problems of the abrasive papers and cloths.
In order to eliminate the above noted defects, various attempts have been made until now. For example, there have been proposed an abrasive wheel comprising an abrasive material contained in a partial formal product of a PVA resin, an abrasive element in which fragments comprising melt spun fibrous materials with fine abrasive grains mixed therewith, are bonded together, an abrasive element made by forming into a various shapes, nonwoven fabric with abrasive material impregnated and bonded thereto, and an abrasive element which is prepared by impregnating a thermosetting resin in pores of an abrasive wheel of a partial formal product of a porous polyvinyl alcohol (e.g., abrasive wheel of a polyvinyl acetal resin) and then hardening the impregnated abrasive wheel to control the compressive modulus.
However, so far there have been no abrasive elements which has the properties of both abrasive wheels and abrasive papers and cloths.
Therefore, there has been a continuous research in the field of abrading and grinding to develop abrasive elements which are flexible like abrasive papers and cloths and have following-up fittness to workpieces, and in which cutting blades of abrasive elements can easily be reproduced and exchanged in order to maintain good sharpness of abrasive wheels.
The present inventors have made intensive studies on foamed abrasive elements and found that a foamed abrasive element comprising a bond of crosslinked and hardened unsaturated polyester resin and having a porosity and a compressive modulus in a certain range, has an excellent following-up fittness, abrasive efficiency, and autogenous action of cutting blade, and, in addition, possesses properties of both abrasive wheels and abrasive papers and cloths. As a resfult the present invention has been accomplished.